The present invention relates to a wave absorber which has an excellent wave absorption characteristic in high frequency bands and is lightweight, compact and nonflammable.
A ferrite utilizing magnetic loss, one impregnating carbon or the like which has dielectric loss into a urethane, one forming these into a pyramid shape or triangular prism shape (hereafter referred to as a "carbon impregnation type"), and the like have been produced as wave absorbers. A wave absorber wall formed by aligning wave absorbers without gaps in a reflective plane surface has been applied in darkrooms where there is to be no refection of radio waves.
The above carbon impregnation type, because the urethane is formed in a pyramid shape or triangular prism shape, has the problems of its tip portion deforming over time, being easily flammable, etc. Although coating with a flame resistant can be performed to increase flame resistance, replacement is necessary every few years over which changes over time are large.
Incidentally, although a wave absorber normally requires a wave absorption factor of 20 dB or more as its wave absorption characteristic, in the case of a carbon impregnation type only, the wave absorption characteristic has such problems as being low in low frequency bands (30 MHz to 50 MHz), leading to the wave absorber having a thickness of 1 m or more, etc. In the case of a ferrite tile having a thickness of 6 to 8 mm, the band width at which it exhibits an absorption of 20 dB or more is a maximum of 30 MHz to 600 MHz or thereabouts, while in the case of a combination of a ferrite and a carbon impregnation type, there is the problem that the thickness is 60 cm or more.
Dark rooms are classified as anechoic rooms for measuring electromagnetic noise emitted from electronic machinery and fully anechoic rooms for testing the noise resistance of electronic machinery etc. In noise resistance tests, because a strong electric field is used, there is the problem of the wave absorber igniting, therefore it is extremely important that the wave absorber be nonflammable.
Also, as the thickness of the wave absorber increases, significant problems such as the effective area within the dark room or the like becoming narrower, the size of the construction becoming larger, and an increase in land allocation and construction costs are incurred.
Further, in recent years diversification of radio wave utilization has spread to the microwave range as typified by microwave ovens and portable wireless, and the necessity for a wave absorber and also a dark room which are effective even in the microwave range from 10 GHz to about 20 GHz as one countermeasure against radio wave pollution has greatly increased.